Rationale: The collateral circulation is tissue- and life-saving in obstructive arterial disease. Disappointing outcomes in clinical trials aimed at augmenting collateral growth highlight the need for greater understanding of collateral biology.

Objective: The role of endothelial nitric oxide synthase (eNOS) in forming native (preexisting) collaterals and remodeling in obstructive disease are unknown or controversial issues, respectively.

Methods and Results: We compared the native collateral circulation in healthy tissue and collateral remodeling after femoral artery ligation (FAL) in wild-type and eNOS-knockout (KO) mice. Perfusion after FAL fell further in adult eNOS-KOs, in association with fewer native collaterals in hindlimb (confirmed in brain). This was not attributable to impaired collateral formation in the embryo-neonate, but rather from collateral loss during growth to adulthood. Compared to wild-type, eNOS-KOs evidenced reduced collateral remodeling, angiogenesis, and flow-mediated dilation of the arterial bed supplying the collaterals, resulting in lower perfusion and greater ischemic injury at all time points over 21 days following FAL. To probe the mechanism for impaired remodeling, we performed genome-wide expression profiling of isolated, remodeling hindlimb collaterals 24 hour after FAL. Upregulation of genes encoding cytokines/chemokines, inflammatory, stress response, and cell cycle proteins was evident in wild-type mice. In contrast, expression was lower in 40 of 44 cell cycle genes in eNOS-KO mice, in association with impaired proliferation of vascular wall cells.

Conclusions: Our findings suggest a novel role for eNOS in maintaining native collateral density during natural growth to adulthood and in collateral remodeling in obstructive disease, the latter through regulation of cell proliferation.